1. Field of the Invention
The present invention relates to an exposure apparatus and an exposure method available for exposure of a mask pattern on a photosensitive substrate during the manufacture of, for example, semiconductor elements or liquid crystal display elements, and particularly to an exposure apparatus equipped with an automatic focusing mechanism and an exposure method utilizing the exposure apparatus.
2. Related Background Art
FIG. 1 is a schematic view showing the structure of a conventional exposure apparatus.
In FIG. 1, a pattern formed on a fixed mask (e.g., reticle) 121 is transferred to a substrate 123 through a projection optical system 122. Here, detection of the focus or positional detection on the image formation surface of the projection optical system has been performed only on the substrate 123 using a focus-detecting optical system for exposure substrates.
With the focus-detecting optical system mentioned above, light emitted from a light source 101, such as an LED, travels via a lens 102 and a visual field slit 103, and is reflected by a mirror 104. The light reflected by the mirror 104 advances through an aperture stop 105 and a lens 106 to strike a mirror 107.
The light reflected by the mirror 107 falls on a substrate 123 obliquely, and strikes a mirror 107' due to specular reflection. The light reflected by the mirror 107' passes through a lens 106' and an aperture stop 108 to strike a mirror 109. The light reflected by the mirror 109 is received by an image sensor 111.
In FIG. 1, if the substrate 123 moves upward in the drawing to the location 123' (shown by a broken line in the drawing), then the light-receiving position on the image sensor 111 for the reflected light from the substrate 123 is displaced downward in the drawing.
Therefore, the upward or downward displacement of the substrate 123 in the drawing may be detected based on the light-receiving position for the reflected light from the substrate 123, and thus the positioning of the substrate 123 has been controlled so that the reflected light is received at a predetermined point, and consequently the substrate 123 is positioned at a predetermined place. As mentioned above, with conventional exposure apparatuses, detection of the focal point has been made only on the surface of the substrate 123 as the exposure object. Accordingly, if up-sizing the mask 121 involves significant bending of the mask 121 due to its own weight or slanting (tapering) of the surface because of a manufacturing error, then detection of the focal point only on the substrate 123, or the exposure object, has inconveniently failed to prevent the occurrence of defocusing of the transferred pattern due to the bending or tapering of the mask 121.